The invention relates to a method for load control, the method being used in a radio system comprising at least one base station and a subscriber terminal which communicate with each other by transmitting and receiving signals representing desired signals and interferences.
The invention further relates to a method for load control, the method being used in a digital radio system comprising at least one base station and a subscriber terminal which communicate with each other by transmitting and receiving signals which are desired signals and/or interferences.
The invention also relates to a radio system comprising at least one base station and a subscriber terminal which comprise at least one transceiver and which are arranged to communicate with one another by transmitting and receiving signals which are desired signals and/or interferences.
The invention further relates to a radio system comprising at least one base station and a subscriber terminal which comprise at least one transceiver and which are arranged to communicate with one another by transmitting and receiving signals which are desired signals and/or interferences.
The invention is applied to interference limited cellular radio systems and particularly to a CDMA system. In the CDMA technique the user""s narrowband data signal is modulated by a spreading code, which is more wideband than the data signal, to a comparatively wide band. In the methods, bandwidths from 1 to 50 MHz have been used. The spreading code is conventionally formed from a long pseudo-random bit sequence. The bit rate of the spreading code is much higher than that of the data signal. In order to distinguish spreading code bits from data bits and symbols comprising bits and combinations of bits, the spreading code bits are called chips. Each user data symbol is multiplied by the spreading code chips. Then the narrowband data signal spreads to the frequency band used by the spreading code. Each user has his/her own spreading code. Several users transmit simultaneously on the same frequency band and the data signals are distinguished from one another in the receivers on the basis of a pseudo-random spreading code.
The capacity of interference limited multiple access systems such as the CDMA cellular radio system is determined by an interference power caused by users. In such a system the subscriber terminal usually establishes a connection with the base station to which the path loss is the smallest. The base station coverage does not in all situations correspond to the traffic need, but the load of some base stations increases to such an extent that the connections to the subscriber terminals can be disconnected either due to the increased interference or to the inadequacy of the transmission capacity.
It is assumed in prior art handover and power regulation algorithms that a connection is established with the base station to which the path loss is the smallest. Such a best connection principle is thus preferable, as the traffic load towards the base station is constant or when the signal-to-interference ratio of the most loaded base station meets the minimum requirement. But when the load of a base station increases to such an extent that the minimum requirements of the connection quality cannot be met, a way is needed to balance the load. A prior art radio system does not, however, allow load management that balances the load, but prior art systems easily lead to an unstable situation, in which disconnecting the connection to some subscriber terminals is the only possibility. Such heavy load situations, in which the connection quality declines below the minimum requirements and which can thus be called overload situations, are not desired.
In the interference limited radio systems it is of primary importance to keep the load sufficiently low, because otherwise owing to fast power control the transmitters increase their power to the maximum. At worst this, in turn, could lead to the disconnecting of most radio system connections. Then again, it is appropriate to handle simultaneously as many connections as possible.
An object of the present invention is to implement a method and a radio system applying the method, in which a load can be optimally controlled at a connection and/or cell level, and thus prevent overload situations and improve the connection quality in a normal situation. Another object of the invention is also to enable large data transmissions using the highest possible data rate.
This is achieved with the method of the type set forth in the preamble characterized by forming a combined signal strength of one or more desired signals; forming a combined total strength of the interferences and one or more desired signals; forming a load result measuring the load by comparing the signal strength and the total strength; comparing the load result with a threshold value, which is a predetermined measure for the highest load level allowed, whereby, when the load result and the threshold value substantially differ from one another, the load is balanced by changing the telecommunication rate.
The method of the invention is further characterized by forming signal-specifically one or more desired signal-to-interference ratios; forming a combined load result of the signals by proportioning one or more desired signal-to-interference ratios with corresponding signal bandwidths and data transmission rates; comparing the load result with a threshold value, which is a predetermined measure for the highest load level allowed, whereby, when the load result and the threshold result substantially differ from one another, the load is balanced by changing the telecommunication rate.
The radio system of the invention is characterized by comprising signal means to form a signal strength of one or more desired signals; total strength means to form a combined total strength for both interferences and one or more desired signals; comparing means to form a load result by comparing the signal strength and the total strength; threshold means to compare the load result with a threshold value, which is a predetermined measure for the highest load level allowed, and when the load result and the threshold value substantially differ from one another on the basis of the comparison, the radio system is arranged to balance the load by changing the telecommunication rate.
The radio system of the invention is further characterized by comprising signal-to-interference ratio means in which one or more desired signal-to-interference ratios are signal-specifically stored; frequency band means in which information on a bandwidth of one or more signals is stored; data transmission rate means which are arranged to form information on a data transmission rate of one or more signals; multiplication means which are arranged to form a load result by proportioning said desired signal-to-interference ratio with said signal bandwidth and data transmission rate; threshold means to compare the load result with a threshold value, which is a predetermined measure for the highest load result allowed, and when the load result and threshold value substantially differ from one another on the basis of the comparison, the radio system is arranged to balance the load by changing the telecommunication rate.
Great advantages are achieved with the method of the invention. The overload situations of an interference limited radio system can be avoided and the load can be optimally controlled. In addition, unstable situations and connection cut-offs can be avoided at the same time as a maximum bit rate can be used in relation to each situation.